Plasma concentrations of gamma-amino butyric acid throughout human gestation

Objective: Normal pregnant women are characterized by decreases in blood pressure and dramatic falls in systemic vascular resistance. This vasodilation is lost in pregnancies complicated by proteinuric hypertension (preeclampsia). Because gamma-amino butyric acid (GABA) is considered to be both an inhibitory neurotransmitter and an antihypertensive amino acid, we hypothesized that GABA levels might increase throughout gestation and might play a role in the vasodilatory alterations observed in normal pregnancy. Methods: Blood samples for measurement of plasma GABA by high-pressure liquid chromatography (HPLC) were obtained from 4 normal nonpregnant women, from 39 pregnant women at various times throughout gestation, and from 5 women with preeclampsia (37-40 weeks). Results: Normal pregnancy was associated with progressive increases (p < 0.01) in plasma GABA levels after the first trimester, reaching maximum values by 27-33 weeks of gestation. In term hypertensive pregnant women, GABA levels were 13 ± 3% lower (p < 0.048) as compared to gestational age-matched controls. During the second and third trimesters of pregnancy, alterations in plasma GABA levels generally mirror changes in plasma volume and correspond inversely with known cardiovascular changes, for example, decreases in blood pressure and especially systemic vascular resistance. Conclusions: These changes in plasma GABA concentrations suggest a potential role for GABA in modulating cardiovascular adaptations in normal pregnancy and a possible role in the development of pregnancy-induced hypertension.